Charles's Law Calculator

Charles's law captures the familiar fact that gases expand when heated and contract when cooled, made precise, and this calculator solves it for whichever quantity you are missing. Choose what you want to find, the initial or final volume, or the initial or final temperature, enter the three values you know, and it returns the fourth, updating as you type. The law states that for a fixed amount of gas held at constant pressure, the volume is directly proportional to the absolute temperature, so the ratio of volume to temperature stays the same. Double the absolute temperature and the volume doubles; halve it and the volume halves. That is the equation volume one over temperature one equals volume two over temperature two, and rearranging it gives any single unknown from the other three. The one rule that must not be broken is that the temperature has to be absolute, measured in kelvin from absolute zero, because the proportionality only works from that true starting point; using Celsius gives badly wrong answers, especially near and below freezing, so remember to add 273.15 to any Celsius value first. The physics is easy to picture: heat the gas and its molecules move faster and strike the walls harder, so at constant pressure the gas must take up more room. This is why a balloon shrinks in the cold and swells in the warmth, why hot-air balloons rise, and why car tyres read higher pressure after a long drive. That makes the tool genuinely useful for chemistry and physics students learning the gas laws and checking homework, and for anyone solving a real volume-and-temperature problem. The formula and a worked example are explained clearly below.

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Temperatures must be in kelvin (add 273.15 to Celsius).